Membrane-enabled heat pipe

ABSTRACT

A modified heat pipe is provided which moves heat from a relatively elevated location to a relatively depressed location and which utilizes osmosis membranes to enable pumping of working fluid to the vaporizer after it has condensed in the condenser.

BACKGROUND OF THE INVENTION

Heat pipes are devices capable of moving thermal energy from one point to another by using a reversible phase change in the state of matter to store and deliver energy. Heat pipes contain at least one reservoir of a volatile substance called the working substance, or working fluid when it is a liquid, at its partial pressure in a closed vessel. The input of thermal energy to this reservoir causes nearly instantaneous vaporization of the substance in the vessel. Once the substance is in its vapor state, it contributes to the overall pressure in the vessel, and can increase the temperature of the vapor throughout the vessel. Subsequent condensation of vapor in potentially distal regions of the vessel transfers the heat of vaporization to the condensation point, effectively transferring energy from the vaporization point to the condensation point.

Generally speaking, heat pipes comprise four universal operating regions. The vaporizer is a region in which heat is transferred into the working substance, generating a state change. The condenser is a region in which heat is transferred out of the working substance, generating a reverse state change. An outgoing pathway is the pathway that energy takes to move from the vaporizer to the condenser, carried by the working substance in the vapor state. A return pathway is the pathway the working substance takes to return from the condenser to the vaporizer.

Many heat pipes contain wicking systems within them. These systems utilize capillary action of the material/working fluid combination to move working fluid from a lowest point in the system to higher points. These systems represent a method of overcoming gravity and distributing the working fluid to areas that are gravitationally higher in energy than the lowest point. Energy can then be absorbed at these points, initiating the phase change and subsequent energy transfer. Some heat pipes that have wicking systems are known as Perkins tubes, after the inventor of the first such system.

Solar thermal systems are systems that utilize solar energy to generate an elevated temperature in comparison to ambient temperature as a first step in achieving any one of a variety of purposes. Among these are heating of water used in household or industrial processes or in heating applications.

Two classes of solar thermal water heating systems are passive and active systems. In passive systems, the heating of a reservoir of water is done by purely passive means. These can include thermosyphon systems, where the heated water itself induces a current flow in the reservoir that brings cooler water to the heating surface and moves heated water away from the heated surface. Such systems are generally restricted to heating reservoirs that are located at higher elevations than the heating surface. Passive systems are not generally desirable for uses in which the collection point of energy is higher than the reservoir.

A second class of solar thermal water heating systems is active systems. In such systems, a pump is used to move a working fluid from the collection point to the point of storage or usage of the thermal energy. Many times, a controller is used which compares the temperatures of the two points and initiates the pump action when the collection point's temperature exceeds the destination point's temperature. These systems are complicated and have more points of failure than the passive systems. Not only might the controller and pump fail, but the power system supplying either or both can fail, generating a total failure in the system. Yet, these systems are more suitable for collecting thermal energy at locations that are elevated relative to the water reservoirs than passive systems.

Solar thermal systems utilize a number of different solar capture systems. Solar energy capture systems are systems that absorb incident solar radiation and transform it into another form of energy, most generally heat or electricity. Solar thermal energy capture systems are systems that capture incident solar radiation, or some fraction thereof, and transform it into heat. Many domestic systems utilize solar thermal energy capture systems constructed using borosilicate glass tubes. These are known as evacuated tube collectors, and typically contain two layers of borosilicate glass tubes with a high vacuum between them. On the interior of the central tube is a copper heat pipe that is painted black so as to absorb incident solar energy and transform it to heat. The copper heat pipe is generally immersed in a liquid water flow that carries heated water to a water tank elsewhere in the structure.

Flat panel solar thermal energy capture systems also exist which may or may not use vacuum insulation. These solar collectors may be built with snaking piping passing over a blackened surface through which water flows. The water absorbs thermal energy that has been absorbed from incident solar radiation by the surface and transports the heat back to a reservoir elsewhere in the structure. Alternatively, these plates may be large heat pipes that capture large amounts of incident solar radiation, transfer this energy as heat to a working fluid, and provide it to a secondary system.

Still other solar thermal energy capture systems use parabolic mirrors or large arrays of mirrors to focus large amounts of solar radiation on a relatively small area, generating high temperatures of up to many hundreds of degrees Celsius. These may be focused on a system of pipes that contain liquids such as water, oils, molten sodium, or other working fluids to absorb and transport the energy either after being pumped or as part of a heat pipe.

Despite these high energy and sophisticated solar thermal energy capture systems, some solar thermal energy capture systems may be surprisingly low tech. For instance some capture systems consist of glass jars filled with black marbles, while others may be black plastic bags or long black tubes. The main requirement for solar energy capture systems is that they are capable of capturing incident solar radiation and transforming it to thermal energy. Generally, they are black. What is done with the energy is also equally varied.

One significant problem with distillation systems is the problem of contamination of the distillate by liquid being distilled. Often times, boiling can lead to quantities of undistilled liquid being pushed into the distillation chamber. The result is that the distilled water contains small amounts of contamination. In order to limit this phenomenon, a number of devices known as liquid-vapor separators have been designed to separate vapor from liquid.

Simple liquid-vapor separators use gravity to separate the liquid from the vapor, with the liquid naturally falling under the action of gravity and the vapor continuing out the top of the separator. Other designs may use ball bearings or glass spheres to physically block the pathway between the input of the liquid-vapor mixture and the vapor outlet. Some more complex designs may use centrifugal forces to move the liquid to the exterior of a spinning vessel while allowing vapor to move to the interior and then out.

The present invention is an innovative heat pipe design. The innovation lies in the addition of an osmosis membrane to the heat pipe, and the use of a solution as a working fluid within. The combination of the two innovations allows the heat pipe to return the working fluid to an elevated location relative to the condensation point, achieving the same function as a wicking system. However, unlike the wicking system, the membrane system may achieve very high flow rates, and can be expanded easily so as to increase flow rates needed for larger energy transfer rates. Moreover, with no moving parts or electronics, the maintenance of the system is significantly simpler than with a more complex electromechanical system. Finally, as vaporization happens only in the vaporizer, the heat transfer is unidirectional to the heat reservoir rather than bidirectional, and so does not need flow controllers or temperature monitors.

Used as a solar system in which the vaporizer is a solar thermal energy capture system, the system allows the capture of solar thermal energy and transport of that energy to a remote location. The system allows for the capture of solar energy and its use in a variety of applications including water heating, home heating, and cooking.

As the system performs an internal distillation, it may be advantageous for the system to include a liquid-vapor separator to limit internal contamination with non-distilled liquid.

SUMMARY

The Summary and Abstract summarize some aspects of the present invention. Simplifications or omissions may have been made to avoid obscuring the purpose of the disclosure. These simplifications or omissions are not intended to limit the scope of the present invention.

In the preferred embodiment of the invention, an apparatus for transferring heat from a location of relatively higher elevation to one of relatively lower elevation is disclosed. This apparatus functions, similarly to conventional heat tubes, by absorbing heat at one location and transferring the heat to a second location through opposite state changes in a working fluid contained within. The working fluid is a solution comprising a pure fluid and one or more dissolved solutes. The condensed working fluid contains little or no dissolved solids. This condensed working fluid falls under the action of gravity or through other passive means (which might include centrifugal behavior) to an osmosis membrane assembly. The assembly retains the condensed liquid on one side of an osmosis membrane and the working fluid on the other. A forward osmosis process moves the liquid through the membrane, generating the pressures needed to return the working fluid to the vaporizer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates the general design of a membrane-enabled apparatus for the movement of thermal energy from a location of relatively higher elevation to a second location of relatively lower elevation.

FIG. 2 illustrates the application of a membrane-enabled apparatus for the movement of solar thermal energy from a location of relatively higher elevation to a second location of relatively lower elevation.

FIG. 3 illustrates a design of the membrane assembly.

DETAILED DESCRIPTION OF DRAWINGS

A specific embodiment of the invention will now be described in detail with reference to the accompanying figures.

In the following detailed description of the preferred embodiment of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment. Furthermore, the referenced embodiment is not necessarily mutually exclusive of other embodiments.

One objective of the invention is to transfer heat from a location of relatively higher elevation to a second location of relatively lower elevation.

FIG. 1 shows a simplified view of an apparatus for transferring heat from a relatively higher elevation to a second location of relatively lower elevation, in accordance with one embodiment of the apparatus. In a preferred embodiment, the apparatus comprises six principle components: a vaporizer (1), a heat exchanger (5), a membrane assembly (3), a liquid conveyance conduit (2), a vapor return conduit (4), and a liquid-vapor return conduit (6).

All parts of the system are sealed so as to allow a vacuum to be maintained within the apparatus.

The vaporizer (1) is connected to the liquid conveyance conduit (2), and, in operation, is partially filled with a working solution that also fills the liquid conveyance conduit (2) and part of the membrane assembly (3). The vaporizer (1) transfers heat applied to either the exterior or interior of the vaporizer (1) by means of an external heat source or an internal heater or other source of thermal energy to the working fluid, causing its vaporization. The vapor produced moves out of the vaporizer through the vapor return conduit (4). The vapor return conduit (4) is connected to the heat exchanger (5) in such a way that the vapor can naturally flow into and through the heat exchanger (5) and on to the liquid-vapor return conduit (6). On the way through the heat exchanger (5), some of the vapor condenses, transferring heat out of the apparatus. The liquid then falls under the action of gravity into the liquid-vapor return conduit (6) and continues on into the membrane assembly (3). The membrane assembly (3) is constructed in such a way that its interior is separated into two chambers, with the membrane itself forming part of the barrier between the two chambers. The condensed liquid comes into contact with one side of the membrane, and the working solution is in contact with the other side of the membrane. In the event that the concentration of dissolved solutes differs on the two sides, a forward osmosis will occur. As the condensed liquid contains relatively few dissolved solutes, the forward osmosis will occur in such a way as to move the condensed liquid through the membrane in the membrane assembly (3) and into the solution, providing the pressure required to return the solution to the vaporizer (1).

FIG. 2 shows a simplified view of an apparatus for transferring heat from a relatively higher elevation to a second location of relatively lower elevation, in accordance with a second embodiment of the apparatus.

In a preferred embodiment, the apparatus comprises eight principle components: a solar vaporizer (1), a heat exchanger (5), a membrane assembly (3), a liquid conveyance conduit (2), a vapor return conduit (4), a liquid-vapor return conduit (6), a liquid-vapor separator (7), and a solution return conduit (8).

All parts of the system are sealed so as to allow a vacuum to be maintained within the apparatus.

The solar vaporizer (1) is connected to the liquid conveyance conduit (2), and, in operation, is partially filled with a working solution that also fills the liquid conveyance conduit (2) and part of the membrane assembly (3). The vaporizer (1) absorbs solar energy in the form of heat and transfers the heat applied to the working fluid, causing its vaporization. The vapor produced moves out of the vaporizer and into the liquid-vapor separator (7), generally carrying with it small to significant amounts of solution. This solution is separated from the vapor in the liquid-vapor separator (7). The solution returns to the vaporizer through a solution return conduit (8) while the liquid continues on into the vapor return conduit (4). The vapor return conduit (4) is connected to the heat exchanger (5) in such a way that the vapor can naturally flow into and through the heat exchanger (5) and on to the liquid-vapor return conduit (6). On the way through the heat exchanger (5), some of the vapor condenses, transferring heat out of the apparatus. The liquid then falls under the action of gravity into the liquid-vapor return conduit (6) and continues on into the membrane assembly (3). The membrane assembly (3) is constructed in such a way that its interior is separated into two chambers, with the membrane itself forming part of the barrier between the two chambers. The condensed liquid comes into contact with one side of the membrane, and the working solution is in contact with the other side of the membrane. In the event that the concentration of dissolved solutes differs on the two sides, a forward osmosis will occur. As the condensed liquid contains no dissolved solutes, the forward osmosis will occur in such a way as to move the condensed liquid through the membrane in the membrane assembly (3) and into the solution, providing the pressure required to return the solution to the vaporizer (1).

FIG. 3 illustrates a design of the membrane assembly (3) wherein the assembly is separated into two chambers known as the solution chamber (9) and the distilled liquid chamber (11). The solution chamber is typically filled with a solution made up of a solvent and solute, and in liquid communication with the vaporizer through the liquid conduit (2). Condensed solvent enters the distilled liquid chamber (11) from the liquid-vapor return conduit (6). When both liquids are in contact with the membrane (10) which forms part of the border between the two chambers, forward osmosis occurs as long as the concentrations of the two solutions differ. This last condition easily follows from the presence of distilled solvent on one side. 

What is claimed is:
 1. An apparatus for moving thermal energy from a location of relatively higher elevation to a location of relatively lower elevation comprising: a membrane assembly comprising an external housing, one or more osmosis membranes, and two internal cavities, hereinafter known as the solution cavity and the distilled liquid cavity, wherein said osmosis membrane(s) forms (form) at least part of the barrier separating the two internal cavities; a vaporizer capable of transferring thermal energy into a working fluid contained therein; a heat exchanger capable of transferring thermal energy out of the working fluid; a liquid conduit connecting said solution cavity of said membrane assembly to said vaporizer; a vapor conduit connecting said vaporizer to said heat exchanger; a liquid-vapor conduit connecting said heat exchanger to said distilled liquid cavity of said membrane assembly; wherein said membrane assembly, liquid conduit, vaporizer, vapor conduit, heat exchanger, and liquid-vapor conduit are sealed so as to enclose a single contiguous volume and so as to enable the maintenance of a vacuum on the interior of the apparatus; wherein a working solution of a solvent and some quantity of solute are contained within the contiguous volume contained by said solution cavity of said membrane assembly, said liquid conduit, and said vaporizer; wherein the application of a quantity of thermal energy to said vaporizer induces a phase change in the solvent of said working solution, transforming it into vapor; wherein said vapor produced in said vaporizer may freely flow throughout the contiguous volume contained by said vapor conduit, said heat exchanger, said liquid-vapor conduit, and said distilled chamber of said membrane assembly excluding that volume occupied by liquid; wherein the condensation of said vapor of said solvent within said vapor conduit, said heat exchanger, said liquid-vapor conduit, and said distilled chamber of said membrane assembly transfers a quantity of heat out of said vapor contained in the contiguous volume enclosed by said vapor conduit, said heat exchanger, said liquid-vapor conduit, and said distilled chamber of said membrane assembly, while transforming a quantity of said vapor into liquid; wherein liquid condensed in said vapor conduit, said heat exchanger, said liquid-vapor conduit, and said distilled chamber of said membrane assembly may pass, under the influence of gravity, centrifugal forces, or other means into said distilled liquid cavity of said membrane assembly; and wherein the presence of a solution in said solution cavity of said membrane assembly and some quantity of distilled solvent in said distilled liquid cavity of said membrane assembly induces forward osmosis through said membrane(s) of said membrane assembly which moves said distilled solvent through said membrane(s) of said membrane assembly into said solution cavity of said membrane assembly.
 2. The apparatus of claim 1 wherein said vaporizer is a solar thermal energy capture system.
 3. An apparatus for moving thermal energy from a location of relatively higher elevation to a location of relatively lower elevation comprising: a membrane assembly comprising an external housing, one or more osmosis membranes, and two internal cavities, hereinafter known as the solution cavity and the distilled liquid cavity, wherein said osmosis membrane(s) forms (form) at least part of the barrier separating the two internal cavities; a vaporizer capable of transferring thermal energy into a working fluid contained therein; a liquid-vapor separator; a heat exchanger capable of transferring thermal energy out of the apparatus; a liquid conduit connecting said solution cavity of said membrane assembly to said vaporizer; a liquid return conduit connecting said liquid-vapor separator to said liquid conduit; a vapor conduit connecting said liquid-vapor separator to said heat exchanger; a liquid-vapor conduit connecting said heat exchanger to said distilled liquid cavity of said membrane assembly; wherein said membrane assembly, liquid-vapor separator, liquid return conduit, liquid conduit, vaporizer, vapor conduit, heat exchanger, and liquid-vapor conduit are sealed so as to enclose a single contiguous volume and so as to enable the maintenance of a vacuum on the interior of the apparatus; wherein a working solution of a solvent and some quantity of solute are contained within the contiguous volume contained by said solution cavity of said membrane assembly, said liquid conduit, and said vaporizer; wherein the application of thermal energy to said vaporizer induces a phase change in the solvent of said working solution, transforming it into vapor; wherein said vaporizer is connected to said liquid-vapor separator so that vapor and liquid move out of said vaporizer and into said liquid-vapor separator as a result of the vaporization of liquid within the vaporizer; wherein said liquid-vapor separator separates liquid and/or vapor ejected from said vaporizer, with the liquid moving into said liquid return conduit and vapor continuing on to said vapor conduit; wherein said vapor produced in said vaporizer and separated from liquid in said liquid-vapor separator may freely flow throughout the contiguous volume contained by said vapor conduit, said heat exchanger, said liquid-vapor conduit, and said distilled chamber of said membrane assembly excluding that volume occupied by liquid; wherein the condensation of said vapor of said solvent within said vapor conduit, said heat exchanger, said liquid-vapor conduit, and said distilled chamber of said membrane assembly transfers a quantity of heat and out of said vapor contained in the contiguous volume enclosed by said vapor conduit, said heat exchanger, said liquid-vapor conduit, and said distilled chamber of said membrane assembly, while transforming said vapor into liquid; wherein liquid condensed in said vapor conduit, said heat exchanger, said liquid-vapor conduit, and said distilled chamber of said membrane assembly may pass, under the influence of gravity, centrifugal forces, or other means, into said distilled liquid cavity of said membrane assembly; and wherein the presence of a solution in said solution cavity of said membrane assembly and distilled solvent in said distilled liquid cavity of said membrane assembly induces forward osmosis through said membrane(s) of said membrane assembly which moves said distilled solvent through said membrane(s) of said membrane assembly into said solution cavity of said membrane assembly.
 4. The apparatus of claim 2 wherein said vaporizer is a solar thermal energy capture system. 